1. Field of the Invention
This invention relates generally to liquid sprayers, atomizers, and the like, and more particularly to nebulizers used in liquid chromatograph/mass spectrometers.
2. Description of the Prior Art
Some analytical instruments, such as the liquid chromatograph/mass spectrometer (LCMS), require the conversion of a liquid sample into a fine mist or spray. The liquid chromatograph portion of the LCMS machine separates organic compounds in a liquid sample, while the mass spectrometer portion of the LCMS machine identifies and quantifies the separated compounds. In order for the mass spectrometer portion of the instrument to function properly, the liquid samples containing the organic compounds must be converted into small, uniform droplets.
The device which creates the droplets in a LCMS machine is commonly known as a nebulizer. It has been an accepted fact in the industry that the droplet size produced by the nebulizer is approximately twice the size of the outlet orifice. In consequence, prior art nebulizers for LCMS instruments typically have an outlet orifice diameter of 5 microns and produce droplets approximately 10 microns in diameter.
The small outlet orifice of prior art nebulizer results in a number of problems. For one, prior art nebulizers orifices tend to become clogged by particulate matter or by diabatic freezing as the fluid is released from the nebulizer. Also, prior art nebulizers produce a broad range of droplet sizes which reduces the accuracy of the LCMS instrument. Furthermore, the small orifice size reduces the volume of droplets which can be produced.
Another problem with prior art nebulizers which may be related to their small outlet orifice size is that the nebulizers must be started at atmospheric pressure, and then pumped down to vacuum level pressures. This is apparently due to the fact that the high surface tension of the liquid across the small outlet orifices prevents initial droplet formation under vacuum conditions.